Scope of registry

[Tony Linde]

Continuing the OAI theme: this should be achievable. If, as I suggested
in a previous message, we have a Metadata Format for each resource type
(catalog, archive, dataset, table merge service etc.), then the format
schema for each type will list the fields (with content constraints)
that will be used to describe that resource type.

Many of the resource types will have common fields, eg wavelength,
position, observationType, etc. It will then be possible to submit a
registry query which looks at *all* resource types whose schemas contain
the fields (wavelength, position, observationType). You could also
restrict the query to, say, only return resources of type 'catalog'. You
might also make some of the criteria, eg observationType optional, so
any resource type whose schema does not include observationType (or
where the observationType was included but missing on some records)
would also be included in the search, but only using the first two
criteria.

Once we've got this working, some projects may want to look at ways of
building some intelligence into the interpretation of the schema fields.
Eg, it may be possible to deduce (with a calculable probability factor -
which might be included in the query) one field from combinations of
other fields. The next step will be to bring ontological inference into
the deduction process.

Cheers,
Tony.

> -----Original Message-----
> From: Clive Page [mailto:cgp at star.le.ac.uk] 
> Sent: 07 February 2003 09:38
> To: registry at ivoa.net
> Subject: Re: Scope of registry
> 
> 
> On Thu, 6 Feb 2003, Roy Williams wrote:
> 
> > In the OAI model, there are exactly six verbs that the registry 
> > understands. The verbs are:
> >
> > Identify (who are you)
> > List Metadata Formats (what schemas do you have for metadata) List 
> > Sets (collections hosted by this repository) List 
> Identifiers (return 
> > just the identifiers and dates of most recent
> > change)
> > List Records (return full records)
> > Get Record (return a full record from its identifier).
> >
> > This is a pretty basic set of services!
> 
> That seems to me rather more basic than will be suitable for 
> what we want. I confess to thinking of the registry in 
> database terms.  Users might want to send queries to the 
> registry equivalent to this sort of thing (expressed for 
> convenience in pseudo-SQL):
> 
> SELECT * FROM registry WHERE WAVELENGTH BETWEEN "400 nm" AND 
> "800 nm" AND
>   POSITION("12:34:56,-01:23,10") AND TYPE = "photometry"
> 
> If we don't allow such selectivity in registry queries, won't 
> all queries just return all records?  I thought the idea of 
> the registry was not just to have a definitive list of 
> resources, but also avoid the necessity for users to send 
> their queries to _all_ registered resources, just on the 
> off-chance that each of them might have some information of relevance.
> 
> Querying all resources will be very time-consuming, and will 
> also have to be repeated, because not all resources will be 
> on-line at all times. Users who suspect that the archives of 
> the University of Erewhon Observatory has something relevant, 
> but find that it is frequently off-line will have to try it 
> many times.  If, on the other hand, their initial query to 
> the Registry shows that the answer concerning the Erewhon 
> site is "no" rather than "maybe", they can avoid such 
> time-wasting activities.
> 
> To those who doubt that this is an important factor I would 
> suggest: go to the Astrobrowse site, 
> http://heasarc.gsfc.nasa.gov/ab/, and select a > full search, 
> and see how long it takes to get an answer from all the 
> linked resources.  I find it takes typically 40 to 60 
> seconds, but that sometimes one or two sites never respond 
> (we all have occasional outages, after all).  Astrobrowse 
> currently only queries the principal sites, all 
> well-networked and well-managed.  When our Registry includes 
> sites less well endowed, things may not be as good.
> 
> 
> -- 
> Clive Page,
> Dept of Physics & Astronomy,
> University of Leicester,    Tel +44 116 252 3551
> Leicester, LE1 7RH,  U.K.   Fax +44 116 252 3311
>